Process for producing aromatic primary diamines

ABSTRACT

The present disclosure relates to a process for the production of aromatic primary amines, by reacting an aromatic dialdehyde with hydrogen and ammonia or an ammonia-liberating compound, in the presence of a hydrogenation catalyst and an amine, wherein the molar ratio of the amine to the aromatic dialdehyde is no less than 1:4 at the start of the reaction.

This application is a continuation of U.S. application Ser. No.15/324,932, filed Jan. 9, 2017, which is a U.S. national phase entryunder 35 U.S.C. § 371 of International Application No.PCT/CN2015/083535, filed on Jul. 8, 2015, which claims priority to PCTInternational Application No. PCT/CN2014/081945, filed on Jul. 10, 2014.The entire contents of these applications are explicitly incorporatedherein by this reference.

TECHNICAL FIELD

The present invention relates to a process for producing aromaticprimary diamines by reductive amination of their corresponding aromaticdialdehydes.

BACKGROUND ART

Several processes were known for producing primary diamines fromreductive amination of the corresponding dialdehydes, with ammonia andhydrogen and in the presence of a hydrogenation catalyst.

U.S. Pat. No. 2,636,051 A (SHELL DEV) Apr. 21, 1953 discloses a processfor preparing long-chain aliphatic primary diamines upon conversion ofaliphatic dialdehydes wherein the formyl groups are separated by atleast four carbon atoms, by feeding the aliphatic dialdehyde to areactor containing ammonia, hydrogen and a hydrogenation catalyst at acontrolled flow rate, and provided an example with 60% yield of theprimary diamine product using a Raney nickel catalyst and water solvent.

In a couple of later published patents, such as JP 05-017413 A (KOEICHEM CO LTD) Jan. 26, 1993, JP 07-069999 (CHEM LINZ AG) Mar. 14, 1995,JP 07-196586 A (KURARY CO LTD) Aug. 1, 1995, JP 10-130210 A (KURARAY COLTD) May 19, 1998, JP 10-310559 A (KURARAY CO LTD) Nov. 24, 1998, andU.S. Pat. No. 6,696,609 (KURARAY CO. LTD) Apr. 3, 2003, modifiedprocesses for preparing aliphatic primary diamines (e.g.1,8-octanediamine, 1,9-nonanediamine, and 2-methyl-1,8-octanediamine)were suggested, each using at least one organic solvent replacing thewater solvent applied in U.S. Pat. No. 2,636,051 for a higher diamineproduct yield (86.9% to 96%). These organic solvents include: alcoholicsolvents such as methanol or ethanol; aromatic hydrocarbon such astoluene; and ether solvents such as tetrahydrofuran, 1,4-dioxane, andmethyl-t-butyl ether. Of these organic solvents, U.S. Pat. No. 6,696,609(KURARAY CO. LTD) Apr. 3, 2003 suggested the preference on methanol orethanol, and emphasized that the proportion of primary amine in thereaction mixture should be minimized, in order to produce the desiredaliphatic diamines (i.e. 1,9-nonanediamine and2-methyl-1,8-octanediamine) with a high yield of above 90%.

However, according to a follow-up test conducted by the presentinventors (see Comparative Example 1), the general amination reactionsystem used in the above mentioned patents for converting alphaticdialdehydes is not effective, or rather inapplicable, for reductiveamination of aromatic dialdehydes. In fact, using the same Experimentalprotocol of U.S. Pat. No. 6,696,600, the latest published patentapplication among the above mentioned patents, massive precipitationformed in the reaction system for converting 2,5-diformylfuran (DFF) andno primary diamine product was detected.

In view of the shortcomings of the above-discussed prior art, it is anobject of the present invention to provide an effective process forpreparing aromatic primary diamines from the corresponding aromaticdialdehydes, at a high yield and an economical cost.

Surprisingly and unexpectedly, this object is achieved by the presentinvention using a new process to prepare aromatic primary diamine byreductive amination of its corresponding dialdehyde, which does notdiminish amine presence in the reaction mixture but rather keeps aminimal amine/dialdehyde ratio at the start of the reaction, in order toincrease the product yield.

SUMMARY OF INVENTION

The present invention provides a process for the production of anaromatic primary amine, the process comprising reacting an aromaticdialdehyde with hydrogen and ammonia or an ammonia-liberating compound,in the presence of a hydrogenation catalyst and an amine, wherein themolar ratio of the amine to the aromatic dialdehyde is no less than 1:4at the start of the reaction.

According to the process of the present invention, by keeping a minimalamine/dialdehyde ratio at the start of the reaction, aromatic primarydiamine can be produced in high yields and at an economical cost. Thiseffect, which is a new finding of the present inventors, is contrary tothe prior art teaching on the suppression of primary amine in thereaction mixture to favour the intended reductive amination.Furthermore, the present process can be readily adapted for batch orcontinuous operation mode, thus applicable to a wide range of industrialapplications.

This application claims priority to PCT application No.PCT/CN2014/081945, the whole content of this application beingincorporated herein by reference for all purposes.

The term “amine”, as used herein, refers to an organic compound derivedby replacing one or more of the hydrogen atoms in ammonia by an organicgroup, and includes primary, secondary and tertiary amines. Preferably,the amine used at the start of the reaction in the present process is aprimary amine or a secondary amine, more preferably a primary amine.

According to the present invention, a “primary amine” is a compound ofthe formula RNH₂, a “secondary amine” is a compound of the formulaHNRR′, and a “tertiary amine” is a compound of the formula NRR′R″,wherein R, R′, R″ are each independently an organic radical. The term“aromatic primary amine”, as used herein, refers to an aromatic compoundwhich is also a primary amine.

Unlimited examples of R, R′ and R″ may be independently selected fromthe group consisting of alkyl, cycloalkyl, aryl, heterocyclyl,heteroaryl, alkylcycloalkyl, alkylaryl, alkylheterocyclyl,alkylheteroaryl, and alkoxyalkyl. Preferably, R, R′ and R″ areindependently selected from a group consisting of straight or branched(C1-C10) alkyl, phenyl (C1-C3) alkyl, and heteroaryl (C1-C3) alkyl, eachoptionally substituted with substituents selected from the groupconsisting of halogen, hydroxy, alkoxy, amino, nitro, halogen,cycloalkyl, and alkyl.

In some embodiments of the present process invention, the amine used atthe start of the reaction is a primary amine.

Specific examples of primary amines used at the start of the reaction ofthe present process include methylamine, ethylamine, propylamine,butylamine, pentylamine, hexylamine, benzylamine, cyclohexylamine,ethylene diamine and the like. Preferred primary amine examples notablyinclude methylamine, butylamine, pentylamine, and hexylamine, of whichmethylamine and butylamine are further preferred. Advantageously, it isfound that butylamine generally gives a vapour pressure high enough atlow temperatures in the reaction system, thus permits easy recovery.

Notably, aromatic diamines obtainable from the present process are alsousable as the amine ingredient at the start of the reaction.

Alternatively, the amine used at the start of the reaction in thepresent process is a secondary amine of the formula HNRR′, wherein R andR′ are as defined above.

As another alternative, the amine used at the start of the reaction inthe present process is a tertiary amine of the formula NRR′R″, whereinR, R′ and R″ are as defined above.

Exemplified secondary amines used at the start of the reaction of thepresent process include dimethylamine, diethylamine, diethanolamine,dicyclohexylamine, diallylamine, piperidine, pyrolidine, morpholine,N-methylbenzylamine, dibenzylamine and the like. Preferred secondaryamines used in the present invention include dimethylamine,diethylamine, and N-methylbenzylamine.

Exemplified tertiary amines used in the reaction of the present processinclude trimethylamine, triethylamine, triethanolamine,diisopropylethylamine, tricyclohexylamine, triallylamine,benzyldimethylamine, N-methylmorpholine, N-methyldibenzylamine and thelike. Preferred tertiary amines used in the present invention includetrimethylamine, triethylamine, and benzyldimethylamine.

As used in the present invention, the term “aromatic dialdehyde” refersto a compound having at least one aromatic ring substituted with twoaldehyde groups. The aromatic ring as used herein can be a hydrocarbonor heterocyclic ring, and may be selected from a group consisting ofbenzene, pyrene, furan, thiophene, terthiophene, pyrrole, pyridine,terpyridine, pyridine oxide, pyrazine, indole, quinoline, purine,quinazoline, bipyridine, phenanthroline, naphthalene, tetralin,biphenyl, cyclohexylbenzene, indan, anthracene, phenanthrene, fluorene,and azulene, each being optionally substituted with at least onesubstitution selected from a group consisting of C₁-C₂₄ alkyl, amino,hydroxyl, carboxyl, ester, cyano, nitro, halogen, and oxygen.

Particularly preferred examples of the aromatic dialdehyde used in theinvention include those having at least one furan ring substituted withtwo aldehyde groups, such as 2,5-diformylfuran (DFF) and itsderivatives.

Other examples of the aromatic dialdehyde used in the invention include,notably, phthalaldehyde; isophthalaldehyde; terephthalaldehyde;1,2-naphthalenedicarboxaldehyde; 1,3-naphthalenedicarboxaldehyde;1,4-naphthalenedicarboxaldehyde; 1,6-naphthalenedicarboxaldehyde;1,8-naphthalenedicarboxaldehyde; 2,6-naphthalenedicarboxaldehyde;1,7-naphthalenedicarboxaldehyde; 2,5 -naphtha1enedicarboxaldehyde;1,4-anthracenedicarboxaldehyde; 1,6-anthracenedicarboxaldehyde;1,10-anthracenedicarboxaldehyde; 2,3-anthracenedicarboxaldehyde;2,7-anthracenedicarboxaldehyde; 1,2-anthracenedicarboxaldehyde;1,9-anthracenedicarboxaldhyde; 9,10-anthracenedicarboxaldehyde;1,2-phenanthrenedicarboxaldehyde; 1,4-phenanthrenedicarboxaldehyde;1,9-phenanthrenedicarboxaldehyde; 2,3-phenanthrenedicarboxaldehyde;3,5-phenanthrenedicarboxaldehyde; 9,10-phenanthrenedicarboxaldehyde;4,4′-biphenyldicarboxaldehyde; 3,3-biphenyldicarboxaldehyde;2,3-biphenyldicarboxaldehyde; 2,4-biphenyldicarboxaldehyde;2,6-biphenyldicarboxaldehyde; 2,2″-(p-terphenyl) dicarboxaldehyde;2,3-(o-terphenyl) dicarboxaldehyde; 2,6′-(m-terphenyl) dicarboxaldehyde;1,4′-(o-terphenyl) dicarboxaldehyde; 4,4″-(p-terphenyl)dicarboxaldehyde; 3,3′-(p-terphenyl) dicarboxaldehyde; 2,6-(o-terphenyl)dicarboxaldehyde; and the like.

The above mentioned aromatic dialdehydes are known in the art and can bereadily prepared by, for example, hydrolysis of dihalides, Gattermannscarbon monoxide synthesis using formyl chloride or the equivalentthereof, and oxidation of various aromatic materials.

The present process requires that, at the start of the aminationreaction, the molar ratio of the amine to the aromatic dialdehyde is noless than 1:4, preferably no less than 1:2, and more preferably no lessthan 1:1.

Also preferably, at the start of the amination reaction, the molar ratioof the amine to the aromatic dialdehyde is no more than 4:1, preferablyno more than 3:1, and more preferably no more than 2:1. At the start ofthe amination reaction, the molar ratio of the amine to the aromaticdialdehyde may be then comprised between 1:4 and 4:1, more preferablycomprised between 1:2 and 4:1 (limit inclusive).

Without wishing to be bound to any particular theory, it is believedthat the aromatic dialdehyde reactant was first reacted with amine toform a diimine intermediate, which is then hydrogenated in the presenceof ammonia to form the diamine product in the reaction system.

In the process of the present invention, ammonia or anammonia-liberating compound or mixtures thereof may be used. Examples ofsuch ammonia-liberating compounds include urea, uric acid, ammoniumsalts and derivatives of a primary amide, for example, symmetrical andunsymmetrical carbamates, carbaminates, semicarbazides andsemicarbazoles, or aminium salts or organic/inorganic esters thereof.Preference may be given to using ammonia itself, with liquid or gaseousammonia being able to be used in this embodiment.

As the preferred molar ratio of the aromatic dialdehyde to theequivalents of ammonia, which may be formed from the ammonia introducedand/or the ammonia-liberating compound or the sum of such compounds usedin the process, value in the range of 1:2-1:50 and preferably in therange of 1:5-1:20 may be set.

The hydrogenation catalyst usable for the present process may beselected from Raney catalysts such as Raney nickel, Raney cobalt andRaney copper. Alternatively, said hydrogenation catalyst may be selectedfrom supported catalysts comprising a metal having hydrogenationactivity such as nickel, cobalt, platinum, palladium, rhodium, rutheniumor copper on a support such as Kieselguhr, silica, alumina,silica-alumina, clay, titania, zirconia, magnesia, calcia, lanthanumoxide, niobium oxide or carbon. These hydrogenation catalysts may haveany shape such as powder, grains or pellets. The amount of thehydrogenation catalyst used may vary according to the desired reactionrate, and it is desirably in a range of 0.01 to 30% by weight based onthe weight of the reaction mixture, more preferably in a range of 0.1 to10% by weight on the same basis. The hydrogenation catalyst may be usedin the form of suspension or as a fixed bed. Nickel hydrogenationcatalysts include those commercially available under the tradedesignations “PRICAT 9908”, “PRICAT 9910”, “PRICAT 9920”, “PRICAT 9932”,“PRICAT 9936,” “PRICAT 9939”, “PRICAT 9953”, “PRICAT 20/15 D”, “PRICATNI 52/35”, “PRICAT NI 52/35 P”, “PRICAT NI 55/5 P”, “PRICAT NI 60/15 P”,“PRICAT NI 62/15 P”, “PRICAT NI 52/35 T”, “PRICAT NI 55/5 T” and “PRICATNI 60/15 T” (available from Johnson Matthey Catalysts, Ward Hill, Mass.)(wherein D=droplet, P=powder, and T=tablet). Hydrogenation catalyst mayalso be chosen from nickel catalysts such as Ni/PrO2-CeO2 catalysts andCuNiOx catalysts, optionally comprising another metal such as Zn or Pdfor instance.

Although not specifically limited, the amination reaction of the presentprocess is desirably carried out under a hydrogen partial pressure in arange of 0.1 to 25 MPa, and more preferably in a range of 0.5 to 20 MPa.Optionally, hydrogen may be added during the reaction to make up for theconsumption or continuously circulated through the reaction zone.

Preferably, the amination reaction of the present process is carried outin a liquid phase using a solvent. The solvent used should be liquidunder the temperature and pressure throughout the amination reaction,and substantially inert to the reactants and products in the reactionmixture of the present process. Suitable examples of such solventinclude: alcoholic solvent such as methanol, ethanol, 2-propanol,1-butanol, isoamyl alcohol and n-octyl alcohol; an aromatic hydrocarbonsolvent such as toluene; or an ether solvent such as methyl t-butylether, tetrahydrofuran and 1,4-dioxane, among which methanol and ethanolare preferred.

These solvents may be used in any amount with no specific restrictions,but desirably in an amount ranging from 0.5 to 50 times the weight ofthe aromatic dialdehyde used, and more preferably in an amount of 2 to10 times the weight of the aromatic dialdehyde used.

The reaction temperature is desirably in a range of 40 to 200° C., morepreferably in a range of 100 to 150° C.

The reaction can be carried out either batchwise or continuously. Ineither case, it is recommended to feed the aromatic dialdehyde in amanner to ensure that the molar ratio of amine to the aromaticdialdehyde is no less than 1:4 throughout the reaction, and ispreferably in a range of 1:4 to 2:1, more preferably in a range of 1:1to 2:1.

Suitable reaction vessels for carrying out the amination reaction of thepresent process may be selected from conventional types of autoclavesand conventional types of tubular reactors. Depending on the specificmedium and/or depending on the specific conditions of the respectivereaction, the reactor may be operated under the atmospheric pressure orunder a partial pressure of 0.1-20 MPa, preferably 0.5-10 MPa and morepreferably 1-3 MPa. This pressure may be generated by injected hydrogenand ammonia and/or by pressurization of the reactor with a further,preferably inert gas such as nitrogen or argon and/or by formation ofammonia in situ from an ammonia-liberating compound or mixtures thereofand/or by setting of the desired reaction temperature.

In the present process, the sequence of adding different reactants isnot strictly limited. In one embodiment of the reaction, an aromaticdialdehyde or its solution in a solvent is fed together with ammonia toa reaction vessel filled with a hydrogenation catalyst, amine, a solventand hydrogen. In an alternative embodiment, hydrogen was introduced in areaction vessel containing a premix of an aromatic dialdehyde, amine,ammonia and a hydrogenation catalyst in a solvent. In yet anotherembodiment, the aromatic dialdehyde is dropwise added to a reactionvessel containing a premix of an amine, ammonia, hydrogen andhydrogenation catalyst in a solvent.

The amination reaction of the present process gives an aromatic diaminecorresponding to the dialdehyde used, e.g. 2,5-bis(aminomethyl)furan(FDA) obtained from DFF: p-xylylenediamine from terephthalaldehyde;m-xylylenediamine from isophthalaldehyde andbis(5-amino-2-furfuryl)ether from bis(5-formyl-2-furfuryl)ether.

Of the above mentioned aromatic diamine products, the DFF-converted FDAis of particular interest, since FDA is a frequently used startingmaterial in polyamine, polyamide and polyurethane syntheses, while DFFis widely available from biomass-derived resources.

The aromatic diamine obtained from the amination reaction can bepurified to a high purity by the usual purification procedure comprisingdistilling off ammonia and any present solvent from the reaction mixturefrom which the hydrogenation catalyst has been separated and subjectingthe residue to distillation or recrystallization.

DESCRIPTION OF EMBODIMENTS

Having generally described the invention, a further understanding may beobtained by reference to the examples below, which are provided for thesole purpose of illustration and not intending to limit the invention.Should the disclosure of any patents, patent applications, andpublications which are incorporated herein by reference conflict withthe description of the present application to the extent that it mayrender a term unclear, the present description shall take precedence

EXAMPLES Example 1

To a 100 mL Parr reactor containing 200 mg Raney Co, 2.0 mmol DFF and6.0 mmol N-butylamine was introduced with 25 mL ethanol. The reactor wasthen purged with nitrogen for three times, and the mixture was agitatedunder an ammonia atmosphere (0.2 MPa) to dissolve approximately 2 g ofammonia in the alcohol. Hydrogen was then introduced into the reactor toprovide a hydrogen partial pressure of 2 MPa, and the reaction thenproceeded at a temperature of 150° C. for 3 hours. After completion ofthe reaction, the reactor was allowed to cool down and unreacted ammoniawas released. Analysis of the residual liquid phase in the reactor bygas chromatography revealed that 112 mg of FDA was obtained, giving ayield of 44% based on the DFF used.

Comparative Example 1

Example 1 of U.S. Pat. No. 6,696,609 was reproduced in this ComparativeExample, with identical experimental conditions to supress thegeneration of primary amine in the reaction system.

A 100 ml Parr reactor equipped with a mechanical stirrer was chargedwith 25 ml of methanol and 150 mg of Raney nickel. After being flushedfor three times with nitrogen, the autoclave was then charged with 2 gof ammonia and, while a hydrogen partial pressure of 3 MPa was applied,heated to a temperature of 140° C. Thereafter, a methanolic solutionobtained by dissolving 620 mg (5 mmol) of DFF in 25 ml of methanol wasfed through a high-pressure metering pump to the autoclave over 1 hour.After completion of the feeding, the reaction mixture was stirred foranother 1 hour at 140° C. Massive charcoal-like precipitate was observedto form in the reactor and the GC-MS analysis of the residual solutionshowed that no aminated product was formed.

Example 2

To a 100 mL Parr reactor containing 200 mg Raney Co, 2.0 mmol DFF and6.0 mmol methylamine (in the form of a 40 wt % aqueous solution) wasintroduced with 25 mL methanol. The reactor was then purged withnitrogen for three times, and the mixture was agitated under an ammoniaatmosphere (0.2 MPa) to dissolve approximately 2 g of ammonia in thealcohol. Hydrogen was then introduced into the reactor to provide ahydrogen partial pressure of 2 MPa, and the reaction then proceeded at atemperature of 115-120° C. for 3 hours. After completion of thereaction, the reactor was allowed to cool down and unreacted ammonia wasreleased. Analysis of the residual liquid phase in the reactor by gaschromatography revealed that 97 mg of FDA was obtained, giving a yieldof 33% based on the DFF used.

Comparative Example 3

The operation of Example 1 was repeated in the absence n-butylamine,there was obtained only 18 mg of FDA, corresponding to a yield of 7%based upon the DFF used.

Comparative Example 4

The operation of Example 1 was repeated expect that 0.4 mmoln-butylamine was introduced into the mixture of Raney Co and DFF. Therewas obtained 63 mg of FDA, corresponding to a yield of 25% based uponthe DFF used.

Example 5

The operation of Example 1 was repeated, expect that 2.0 mmoln-butylamine was introduced into the mixture of Raney Co and DFF. Therewas obtained 96 mg of FDA, corresponding to a yield of 38% based uponthe DFF used.

Example 6

To a 100 mL Parr reactor containing 120 mg Pricat Ni 52/35, 2.0 mmol DFFand 6.0 mmol n-butylamine was introduced 25 mL methanol. The reactor wasthen purged with nitrogen for three times, and the mixture was agitatedunder an atmosphere of 0.2 MPa ammonia to dissolve approximately 2 g ofammonia in the alcohol. Hydrogen was then introduced into the reactor toprovide a hydrogen partial pressure of 2 MPa, and the reaction thenproceeded at a temperature of 115-120° C. for 4 hours. After completionof the reaction, the reactor was allowed to cool down and unreactedammonia was released. Analysis of the residual liquid phase in thereactor by gas chromatography revealed that 55 mg of FDA and 44 mg oftertahydrofuran-2,5-dimethylamine (THFDA) were obtained. the yieldsbased on the DFF used are 22% and 17% respectively.

Example 7

To a 100 mL Parr reactor containing 120 mg of a Ni/PrO2-CeO2 catalyst,2.0 mmol DFF and 6.0 mmol n-butylamine was introduced 25 mL methanol.The reactor was then purged with nitrogen for three times, and themixture was agitated under an atmosphere of 0.2 MPa ammonia to dissolveapproximately 2 g of ammonia in the alcohol. Hydrogen was thenintroduced into the reactor to provide a hydrogen partial pressure of 2MPa, and the reaction then proceeded at a temperature of 115-120° C. for4 hours. After completion of the reaction, the reactor was allowed tocool down and unreacted ammonia was released. Analysis of the residualliquid phase in the reactor by gas chromatography revealed that 114 mgof FDA was obtained, giving a yield of 45% based on the DFF.

Example 8

To a 100 mL Parr reactor containing 120 mg of a CuNiOx catalyst, 2.0mmol DFF and 6.0 mmol n-butylamine was introduced 25 mL methanol. Thereactor was then purged with nitrogen for three times, and the mixturewas agitated under an atmosphere of 0.2 MPa ammonia to dissolveapproximately 2 g of ammonia in the alcohol. Hydrogen was thenintroduced into the reactor to provide a hydrogen partial pressure of 2MPa, and the reaction then proceeded at a temperature of 115-120° C. for4 hours. After completion of the reaction, the reactor was allowed tocool down and unreacted ammonia was released. Analysis of the residualliquid phase in the reactor by gas chromatography revealed that 124 mgof FDA was obtained, giving a yield of 49% based on the DFF.

Example 9

To a 100 mL Parr reactor containing 120 mg of a CuNiOx catalyst, 2.0mmol DFF and 6.0 mmol n-butylamine was introduced 25 mL methanol. Thereactor was then purged with nitrogen for three times, and the mixturewas agitated under an atmosphere of 0.2 MPa ammonia to dissolveapproximately 2 g of ammonia in the alcohol. Hydrogen was thenintroduced into the reactor to provide a hydrogen partial pressure of 2MPa, and the reaction then proceeded at a temperature of 80° C. for 15hours. After completion of the reaction, the reactor was allowed to cooldown and unreacted ammonia was released. Analysis of the residual liquidphase in the reactor by gas chromatography revealed that 211 mg of FDAwas obtained, giving a yield of 84% based on the DFF.

The invention claimed is:
 1. A process for the production of an aromatic primary diamine, the process comprising reacting an aromatic dialdehyde, wherein the aromatic ring is a hydrocarbon ring, with hydrogen and ammonia or an ammonia-liberating compound selected from the group consisting of urea, uric acid, ammonium salts, symmetrical and unsymmetrical carbamates, carbaminates, semicarbazides, semicarbazoles, and aminium salts and organic/inorganic esters thereof, in the presence of a hydrogenation catalyst and an amine, wherein the molar ratio of the amine to the aromatic dialdehyde is no less than 1:4 at the start of the reaction.
 2. The process of claim 1, wherein the amine is selected from a group consisting of methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, benzylamine, cyclohexylamine, ethylene diamine, dimethylamine, diethylamine, diethanolamine, dicyclohexylamine, diallylamine, piperidine, pyrolidine, morpholine, N-methylbenzylamine, dibenzylamine, trimethylamine, triethylamine, triethanolamine, diisopropylethylamine, tricyclohexylamine, triallylamine, benzyldimethylamine, N-methylmorpholine, and N-methyldibenzylamine.
 3. The process of claim 1, wherein the aromatic ring is benzene.
 4. The process of claim 1, wherein the aromatic diamine is m-xylylenediamine and the aromatic dialdehyde is isophthalaldehyde.
 5. The process of claim 4, wherein the amine is a primary amine or a secondary amine.
 6. The process of claim 5, wherein the amine is a primary amine.
 7. The process of claim 6, wherein the primary amine is selected from a group consisting of methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, benzylamine, cyclohexylamine, and ethylene diamine.
 8. The process of claim 4, wherein the amine is a secondary amine selected from the group consisting of dimethylamine, diethylamine, diethanolamine, dicyclohexylamine, diallylamine, piperidine, pyrolidine, morpholine, N-methylbenzylamine, and dibenzylamine.
 9. The process of claim 4, wherein the amine is a tertiary amine selected from a group consisting of trimethylamine, triethylamine, triethanolamine, diisopropylethylamine, tricyclohexylamine, triallylamine, benzyldimethylamine, N-methylmorpholine, and N-methyldibenzylamine.
 10. The process of claim 4, wherein the molar ratio of the amine to isophthalaldehyde is no less than 1:1, at the start of the reaction.
 11. The process of claim 4, wherein the molar ratio of the amine to isophthalaldehyde is no more than 3:1 at the start of the reaction.
 12. The process of claim 4, wherein the molar ratio of isophthalaldehyde to the equivalents of ammonia is in the range of 1:5-1:20.
 13. The process of claim 4, wherein isophthalaldehyde is fed in a manner to ensure that the molar ratio of amine to isophthalaldehyde is in a range of 1:4 to 2:1.
 14. The process of claim 4, wherein the hydrogenation catalyst is Raney copper, Ni/PrO₂-CeO₂, or CuNiOx, optionally comprising another metal Zn or Pd.
 15. The process of claim 4, wherein ammonia is used.
 16. The process of claim 1, wherein the aromatic diamine is p-xylylenediamine and the aromatic dialdehyde is terephthalaldehyde.
 17. The process of claim 16, wherein the amine is a primary amine selected from a group consisting of methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, benzylamine, cyclohexylamine, and ethylene diamine.
 18. The process of claim 16, wherein the amine is a secondary amine selected from the group consisting of dimethylamine, diethylamine, diethanolamine, dicyclohexylamine, diallylamine, piperidine, pyrolidine, morpholine, N-methylbenzylamine, and dibenzylamine.
 19. The process of claim 16, wherein the amine is a tertiary amine selected from a group consisting of trimethylamine, triethylamine, triethanolamine, diisopropylethylamine, tricyclohexylamine, triallylamine, benzyldimethylamine, N-methylmorpholine, and N-methyldibenzylamine.
 20. The process of claim 16, wherein the molar ratio of the amine to terephthalaldehyde is no less than 1:1, at the start of the reaction. 